The brain consists of billions of cells that communicate with each other to produce fundamental processes such as thought and perception and to orchestrate all body functions. At the molecular level, many of these processes are Ca2+-dependent. The long-term objective is to understand the molecular mechanisms underlying Ca2+-dependent processes in the brain with emphasis on 4 aims. (1) To characterize the regulatory properties of cytosolic calmodulin(CaM)-dependent phosphatase and particulate CaM-dependent phosphatase and to compare their molecular and functional properties, (2) to identify the interacting domains of CaM for phosphodiesterase. (3) to elucidate the interacting sites of subunit B with subunit A of CaM-dependent phosphatase, and (4) characterize a novel Ca2+-binding protein (CaBP-20) from bovine brain and a novel Ca2+-binding protein (CaBP-15) from chick brain. These experiments involve purification of several proteins from the brain tissue using standard biochemical techniques, and their characterization. Other techniques include protein chemistry, monoclonal and polyclonal antibodies, and immunocytochemical localization at both the light and the electronmicroscopic levels.